Scalable, Printable, Patterned Sheet Of High Mobility Graphene On Flexible Substrates

ABSTRACT

The present invention provides methods for fabricating graphene workpieces. The present invention also provides for products produced by the methods of the present invention and for apparatuses used to perform the methods of the present invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/752,421, filed Jan. 24, 2020; which is a continuation of U.S. patentapplication Ser. No. 16/214,601, filed Dec. 10, 2018; which is acontinuation of U.S. patent application Ser. No. 15/850,046, filed Dec.21, 2017 (now U.S. Pat. No. 10,165,679, issued Dec. 25, 2018); which isa continuation of U.S. patent application Ser. No. 15/305,167, filedOct. 19, 2016 (now U.S. Pat. No. 9,930,777, issued Mar. 27, 2018); whichis a National Stage Application of International Patent Application No.PCT/US2015/027193, filed Apr. 23, 2015; which claims the benefit of andpriority to U.S. Patent Application No. 61/983,014, filed Apr. 23, 2014.The disclosures of the foregoing applications are incorporated herein byreference in their entireties for any and all purposes.

GOVERNMENT RIGHTS

This invention was made with government support under Contract No.DMR08-32802 awarded by the Nano/Bio Interface NSF NSEC. The governmenthas certain rights in the invention.

FIELD OF THE INVENTION

The disclosed invention is directed toward the fields of grapheneworkpieces and of manufacturing methods thereof.

BACKGROUND

The present application generally relates to methods and apparatus fortransfer of films from one or more substrates to another, where the filmto be transferred is patterned during the transfer step.

Since the first isolation of graphene in 2004, interest in the materialhas surged in the research community and more recently in industry asthe first commercial ventures in graphene production and applicationshave emerged. Graphene is a single atom thick sheet of carbon atomspacked in a honeycomb lattice that has unique properties owing to itstwo-dimensional geometry and aromatic chemical structure. The uniqueband structure of this material shows a linear dispersion relation atlow energies, allowing the holes and electrons to have zero effectivemass and behave like relativistic particles. This leads to impressiveelectrical properties, such as measured mobilities of 200,000 cm²/V−sand ballistic transport on the micrometer scale at room temperature.Additionally, the superior tensile strength of the material allows forhigh electrical performance even under bending and deformation. Due tothese fantastic properties, there has been great interest forapplications in high performance nanoelectronics, flexible electronics,and environmental/biological monitoring applications.

Graphene can be grown in high quality sheets on catalytic metal bychemical vapor deposition at industrial scale, presenting an opportunityfor graphene commercialization that is being pursued by multiplecompanies. In conventional approaches, graphene is coated with a thinpolymer layer (e.g., polymethylmethacrylate—PMMA) to provide mechanicalstability and then removed from a copper growth substrate for transferonto another substrate as a full sheet that may then be patterned intoelectrical devices, etc. There are several disadvantages of this—e.g.,the graphene can be wrinkled during the transfer process since the PMMAlayer is very thin and flexible; the graphene can be contaminated withPMMA residue after cleaning; and the subsequent patterning process canexpose the graphene to chemical contamination. Each of these causes thephysical properties (including the carrier mobility) of the graphene todegrade. Processes are needed for transferring graphene from growthsubstrates to other surfaces while protecting the beneficial propertiesof the material so that it may be used in commercial devices.

Thus, there is a need for processes that enable transfer of graphenefrom growth substrates to other surfaces. There are sets of materials“beyond graphene” (e.g., few-layer graphene, boron nitride, molybdenumdisulfide, other transition metal dichalcogenides, and the like) withsimilar needs for advanced methods of film transfer. The instantdisclosure is directed to these and other important needs.

SUMMARY

The present disclosure provides methods for forming a workpiece, themethods comprising growing pristine monolayer continuous graphene on acatalytic film to form a graphene/catalytic film bilayer, attaching afirst layer of material on top of the graphene surface, and releasingthe graphene from the catalytic film, such that the first layer ofmaterial is sufficiently rigid that it resists folding or tearingthrough the rest of the process. In this way the process ensures thatthe graphene film preserves its very high electronic and structuralquality. In addition, there are sets of materials “beyond graphene”(e.g., few-layer graphene, boron nitride, molybdenum disulfide, othertransition metal dichalcogenides, and the like) with similar needs foradvanced methods of film transfer. The disclosure is directed to theseand other important needs.

The present disclosure also provides workpieces, comprising a substrate,a patterned layer of graphene disposed on the substrate, and a patternedlayer of material disposed on the graphene. The present disclosure alsoprovides electronic devices comprising the workpieces.

The present disclosure also provides workpieces, comprising a substrate,a layer of pristine monolayer continuous graphene disposed on thesubstrate, and a patterned layer of material disposed on the graphene.

The present disclosure also provides workpieces, comprising a patternedlayer of graphene and a patterned layer of a first material disposed onthe graphene.

The general description and the following detailed description areexemplary and explanatory only and are not restrictive of the invention,as defined in the appended claims. Other aspects of the presentdisclosure will be apparent to those skilled in the art in view of thedetailed description of the invention as provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The summary, as well as the following detailed description, is furtherunderstood when read in conjunction with the appended drawings. For thepurpose of illustrating the invention, there are shown in the drawingsexemplary embodiments of the invention; however, the invention is notlimited to the specific methods, compositions, and devices disclosed. Inaddition, the drawings are not necessarily drawn to scale. In thedrawings:

FIG. 1 illustrates an embodiment of the present invention directed to aworkpiece. The workpiece in the upper left has a graphene top layer anda copper bottom layer. The middle left workpiece is the same as the topleft workpiece except it has a polymer layer on top.

FIG. 2 illustrates an alternative embodiment of the present inventiondirected to workpieces on various solid and flexible substrates.

FIG. 3 illustrates exemplary embodiments of the present inventiondirected to workpieces.

FIG. 4 illustrates an exemplary embodiment of the present inventiondirected to workpieces.

FIG. 5(a) illustrates an exemplary embodiment of the present inventiondirected to an electronic device comprising a workpiece.

FIG. 5(b) provides electronic test data of an embodiment of the presentinvention directed to an electronic device comprising a workpiece.

FIG. 6 provides a process whereby an embodiment is directed to anelectronic device comprising a workpiece that is applied to a targetsubstrate. In this figure, the workpiece in the upper left has a toplayer of graphene monolayer and a bottom layer of copper. The middleworkpiece on the left has a top layer of polymer a middle layer ofgraphene monolayer and a bottom layer of copper. The bottom leftworkpiece has a top layer of copper, a second layer of graphenemonolayer, a third layer of polymer and a bottom layer that is thetarget substrate. The workpiece on the right has the target substrate onthe bottom, polymer as the middle layer and graphene monolayer as thetop layer.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention may be understood more readily by reference to thefollowing detailed description taken in connection with the accompanyingfigures and examples, which form a part of this disclosure. It is to beunderstood that this invention is not limited to the specific devices,methods, applications, conditions or parameters described and/or shownherein, and that the terminology used herein is for the purpose ofdescribing particular embodiments by way of example only and is notintended to be limiting of the claimed invention. Also, as used in thespecification including the appended claims, the singular forms “a,”“an,” and “the” include the plural, and reference to a particularnumerical value includes at least that particular value, unless thecontext clearly dictates otherwise. The term “plurality”, as usedherein, means more than one. When a range of values is expressed,another embodiment includes from the one particular value and/or to theother particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another embodiment. All ranges areinclusive and combinable.

It is to be appreciated that certain features of the invention whichare, for clarity, described herein in the context of separateembodiments, may also be provided in combination in a single embodiment.Conversely, various features of the invention that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, reference to values statedin ranges include each and every value within that range.

In one embodiment, the disclosure provides scalable printing-basedmethod for patterning monolayer graphene into arbitrary geometries onflexible polymer substrates while maintaining the high intrinsicmobility of the material (˜10,000 cm²/V−s). In one embodiment of theinvention, a graphene-on-polymer material can be made via a processcomprising laser printing to pattern printer toner onto graphene grownvia chemical vapor deposition on a copper foil substrate to achievewrinkle-free release from the growth substrate. The graphene layer ofthe resulting graphene-on-polymer structure retains the high mobilityand environmental sensitivity characteristic of high-quality graphene,making the structure suitable for use in a number of applications inflexible/foldable electronics, wearable vapor sensors for environmentalmonitoring, printable biosensors for facile medical diagnosis, as wellas inexpensive next-generation energy materials (supercapacitors,transparent electrodes).

In one embodiment, the present invention provides methods of forming aworkpiece. These methods may include growing graphene (e.g., pristinemonolayer continuous graphene) on a catalytic film to form agraphene/catalytic film bilayer. The methods may also include disposinga first layer of material on top of the graphene surface and releasingthe graphene from the catalytic film. In some embodiments, growinggraphene on a catalytic film is performed by chemical vapor deposition(CVD) at either atmospheric or low pressure. The catalytic film cancomprise Cu or Pt foil in some embodiments; catalytic materials that cansupport graphene growth will be known to those of ordinary skill in theart. In some embodiments, the catalytic foil can comprise a roll and thegraphene growing can occur in a “roll-to-roll” system, which mayincorporate a CVD process.

The first layer of material on top of the graphene can be disposed as apatterned or unpatterned layer; in some embodiments it is formed with aprinting process that allows for patterning, e.g., printing on thesurface of the graphene surface with a laser printer, by printing on thesurface of the graphene surface with an inkjet printer with a polymerink, by selective sintering of material (selective heat sintering,selective laser sintering, or both) in a 3D printer, or by selectivelydepositing a liquid binding material in a powder-bed layer of a 3Dprinter. Other printing methods may be used as will be known to those ofordinary skill in the art. The printing process should be engineered soas to avoid damaging or destroying the graphene, which may occur, forexample, through the use of a sintering process that exposes thegraphene to excessively high temperatures in the presence of oxygen.Preferably (though not necessarily), the first layer of material isdisposed and patterned if so desired without the use of a photoresistmaterial as these materials can damage the electronic characteristics ofthe graphene. The first layer of material must be made solid and mustbond to the graphene in order to provide structural support to thereleased graphene. Any printing process which is capable of disposing afirst layer of any material capable of solidifying and bonding to thegraphene is suitable. In some embodiments, a second layer of materialcan be disposed on top of the first layer of material. In preferredmethods, the second layer of material is a substantially unpatternedlayer that does not substantially contact the graphene. The releasing ofthe graphene from the catalytic film can be performed by a bubblingtransfer process, as described by Gao et al., “Repeated growth andbubbling transfer of graphene with millimetre-size single-crystal grainsusing platinum,” Nature Communications 3(2012):699, incorporated hereinby reference in its entirety for all purposes. In methods utilizing asecond layer of material that does not substantially contact thegraphene, the bubbling transfer process results in the removal of allgraphene which is not in contact with the first layer of material. Insome embodiments the method further comprises attaching the releasedgraphene to a substrate, which can comprise one or more of thefollowing: glass, silicon, silicon dioxide, aluminum oxide, sapphire,germanium, gallium arsenide, indium phosphide, an alloy of silicon andgermanium, PET, polyimide, other plastics, or silk. In one preferredembodiment, the substrate comprises Si/SiO₂ and the graphene is attachedto the SiO₂ surface of the substrate.

The present disclosure also provides workpieces. These workpieces mayinclude a substrate, a patterned layer of graphene disposed on thesubstrate, and a patterned layer of a first material disposed on thegraphene. In some embodiments, a workpiece further comprises anunpatterned layer of a second material disposed on the patterned layerof a first material, wherein the unpatterned layer of material does notsubstantially contact the layer of graphene or the substrate. Thesubstrate may comprise one or more of the following: glass, silicon,silicon dioxide, aluminum oxide, sapphire, germanium, gallium arsenide,indium phosphide, an alloy of silicon and germanium, and the like. Theworkpieces preferably comprise graphene with a carrier mobility ofgreater than about 5,500 cm²/V−s. In preferred embodiments, thepatterned layer of a first material disposed on the graphene comprises athickness of less than about 20 micrometers, less than about 10micrometers, or even less than about 5 micrometers. Also furtherpreferred are embodiments wherein the patterned layer of a firstmaterial disposed on the graphene, the unpatterned layer of a secondmaterial disposed on the patterned layer of material, or eachindividually comprises a thickness of less than about 10 micrometers. Insome embodiments the workpieces can comprise a patterned layer of afirst material disposed on the graphene comprises features having acharacteristic dimension of less than about 10 micrometers.

The present invention also provides for electronic devices comprisingthe workpieces described herein. Such an electronic device can mayinclude a workpiece integrated on semiconductor substrates along withelectrode contacts.

The present invention also provides alternative workpieces. Suchworkpieces suitably include a substrate, a layer of graphene (e.g.,pristine monolayer continuous graphene) disposed on the substrate, and apatterned layer of a first material disposed on the graphene. Thesubstrate can comprise a catalytic film that can support graphenegrowth, which comprises Cu or Pt foil in some embodiments; catalyticmaterials that can support graphene growth will be known to those ofordinary skill in the art. In preferred embodiments, the first materialcan comprise a polymer or plastic material. In further preferredembodiments, the first material can comprise a flexible polymer. Inpreferred embodiments, the patterned layer of a first material disposedon the graphene comprises a thickness of less than about 20 micrometers,less than about 10 micrometers, or even less than about 5 micrometers.

In other embodiments, the present invention provides workpieces,comprising a patterned layer of graphene, and a patterned layer of afirst material disposed on the graphene. In some embodiments, theworkpieces further comprise an unpatterned layer of a second materialdisposed on the patterned layer of a first material, wherein theunpatterned layer of a second material does not substantially contactthe layer of graphene. Preferably, the first material, the secondmaterial, or both comprises a flexible polymer. Suitable flexiblepolymers include commercial printer toners, polymer inks, or materialswhich are flexible following disposition via 3-D printing. The patternedlayer of a first material disposed on the graphene, the unpatternedlayer of a second material disposed on the patterned layer of material,or each individually may comprise a thickness of less than about 20micrometers, less than about 10 micrometers, or even less than about 5micrometers.

The disclosure is illustrated by the following non-limiting examples.

Example 1

In one aspect, the present disclosure provides a methods that result inpristine graphene layers on a thin, flexible toner or polymer substratein any desired pattern that can be defined by a printing process.

First, pristine monolayer continuous graphene is grown on a copper filmby chemical vapor deposition (CVD) at either atmospheric or low pressureto create a copper film/graphene bi-layer. Next, the copperfilm/graphene bi-layer is attached to a suitable support and insertedinto a printing apparatus for the attachment of patterned material tothe graphene surface. In one embodiment, the copper film/graphenebi-layer is attached to ordinary printer paper with tape and insertedinto a laser printer. In other embodiments, the copper film/graphenebi-layer is attached to a suitable support for insertion into a 3Dprinter. In yet other embodiments, graphene can be formed on a roll ofcatalytic foil, such as in a “roll-to-roll” process, which can then befed through a printing apparatus. Patterns can be printed successfullywithout damaging the graphene using a variety of printing apparatusesand techniques. These techniques result in a pattern of a solid polymerlayer on the graphene surface. In one embodiment, a conventional laserprinter can be used. Other printing methods include color laser printersand inkjet printing using polymer or polymer-composite inks. In furtherembodiments, a patterned layer of material may be formed on the surfaceof the graphene using a 3D printer, which printer may utilize selectiveheat sintering or selective laser sintering, or alternatively mayutilize selective deposition of a liquid binding material in apowder-bed layer. The printing process should be engineered so as toavoid damaging or destroying the graphene, which may occur, for example,through the use of a sintering process that exposes the graphene toexcessively high temperatures. The printed layer's thickness isdetermined by the printing apparatus used, which can be about around 10micrometers in the case of laser printer toner, although otherthicknesses in the range of from about 500 nm to about 100 micrometersare also suitable; the thickness may be varied as desired for particularapplications. This can be adjusted through engineering of the printingprocess. The line width of the patterning is determined by theresolution of the printer, which can be as small as 1 micrometer, 5micrometers, or even 10 micrometers for the advanced laser printers, forexample. No subsequent processing is needed. There is no need for theuse of photoresist, as the subsequent “bubble method” release step leadsto a patterned graphene layer attached to the thin layer of printedmaterial.

A process for making a workpiece using a conventional laser printer isshown schematically in FIG. 1.

Next, graphene is transferred off of the copper film using suitabletechniques. This can be achieved without applying any additional layersthat provide mechanical backing for the graphene. In some embodiments,the “bubble transfer” method described by Gao et al., “Repeated growthand bubbling transfer of graphene with millimetre-size single-crystalgrains using platinum,” Nature Communications 3(2012):699, incorporatedherein by reference in its entirety for all purposes. Other methods thatdo not apply additional layers that provide mechanical backing for thegraphene are also suitable, e.g., dissolving the catalytic foil. Thegraphene that has the patterned layer of printed material disposed on itthen transfers off the copper foil intact while unsupported graphenedisintegrates during the process. Thus, the material that survives thetransfer process is the patterned graphene-material complex that wascreated during the printing process.

The graphene-on-material structure can be removed from the transfer bathusing tweezers, or a PET sheet, and cleaned with standard processes. Theprinted material acts as a rigid backbone and provides mechanicalsupport to the underlying graphene layer. Workpieces fabricated usingthe method described herein, with a conventional laser printer, and thentransferred to a set of solid and flexible substrates, are shown in FIG.2. Graphene was synthesized on copper catalytic foil to form a copperfilm/graphene bi-layer. The bi-layer was attached with transparent tapeto a sheet of standard 8.5″×11″ paper, with the copper layer facing thepaper and the graphene layer exposed. The paper, with bi-layer attached,was then inserted into a conventional laser printer and a pattern wasprinted with commercial black laser printer toner or color laser printertoner. The workpiece can be curled around an object, such as an objectwith a radius 0.5 mm as shown in FIG. 2. Following release from curling,there were no visible signs of damage, and electrical properties of thegraphene were measured before and after curling, indicating that thecurling process did not degrade the electrical properties. Multipleworkpieces fabricated using the method described herein, with aconventional laser printer, are shown in FIG. 3, which includespatterned graphene-on-polymer workpieces placed onto a glass slide forstorage and later use. Additional workpieces have been fabricated usingthe method described herein with a color laser printer using variouscolored printer toners, which yielded similar results.

Example 2

In some embodiments, a 3D printer is used as in Example 1, with thefurther step of attaching a second layer of material on top of thepatterned layer of material. As in Example 1, pristine monolayercontinuous graphene is grown on a catalytic film by chemical vapordeposition (CVD) at either atmospheric or low pressure to create acatalytic film/graphene bi-layer. Next, the catalytic film/graphenebi-layer is attached to a suitable support and inserted into a 3Dprinting apparatus for the attachment of patterned material to thegraphene surface. In the 3D printer, a patterned layer is disposed onthe graphene surface of the catalytic film/graphene bi-layer.

After the formation of the patterned layer of material, a second,unpatterned layer can be formed on top of the patterned layer ofmaterial. This unpatterned layer may lie across the top of the patternedlayer of material and unsintered or unbound 3D-printer build materialthat is disposed within the pattern. As a result, the unpatterned layercan be disposed on the first layer of patterned material withoutcontacting the graphene. If the “bubble transfer” removal method isused, unsintered or otherwise unbound build material will be removedalong with the disintegrating graphene that has no first layer disposedon it, leaving the patterned graphene matching the first patterned layerof material. In this fashion, the remaining graphene pattern is the sameas one that would result from the process in Example 1, which did notutilize a second unpatterned layer of material. The second, unpatternedlayer is useful for, inter alia, providing more structural support tothe workpiece and allowing for the use of commercial wafter handlingsystems, such as vacuum, suction, or Bernoulli grippers.

Example 3

Graphene-on-polymer samples fabricated as described in Example 1, with aconventional laser printer used to create the patterned layer of polymeron the graphene layer, were evaluated for electrical performance.Samples comprised of a pristine monolayer graphene on a polymer tonerbacking. The samples were curled 360 degrees with a radius of curvatureof less than 1 mm as shown in FIG. 2 without affecting electricalperformance, including carrier mobility.

Sample measurements were conducted using the sample geometry shown inFIG. 5(a), in order to measure the current-gate voltage characteristic(I-Vg) of the graphene layer in a Graphene-on-polymer sample. Themeasurements are consistent with mobilities exceeding 5,000 cm²/V−s,similar to what is intrinsic to CVD-grown graphene. FIG. 5(b) shows atypical I-Vg of a sample after it has been curled around an object witha radius of 0.5 mm. Using a standard model, the inferred mobility isabout 5,500 cm2/V−s. This value is substantially equivalent to thatfound for an identical sample that was not curled, implying that thegraphene properties are unaltered by the curling process.

Terms

The terminology used herein is for the purpose of describing particularaspects only and is not intended to be limiting. For example, the term“comprising” can include the embodiments “consisting of” and “consistingessentially of” Unless defined otherwise, all technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which this disclosure belongs. In thisspecification and in the claims which follow, reference will be made toa number of terms which shall be defined herein.

When ranges are used herein for physical properties or chemicalproperties, all combinations, and subcombinations of ranges for specificembodiments therein are intended to be included.

The disclosures of each patent, patent application, and publicationcited or described in this document are hereby incorporated herein byreference, in its entirety.

Those skilled in the art will appreciate that numerous changes andmodifications can be made to the preferred embodiments of the inventionand that such changes and modifications can be made without departingfrom the spirit of the invention. It is, therefore, intended that theappended claims cover all such equivalent variations as fall within thetrue spirit and scope of the invention.

What is claimed:
 1. A patterned structure comprising: a patterned layer;and a graphene layer coupled to the patterned layer and separated from asubstrate according to a pattern of the patterned layer.
 2. Thepatterned structure of claim 1, wherein the patterned layer providessupport for the graphene layer that is separated from the substrate. 3.The patterned structure of claim 1, wherein the separated graphene layerhas the same pattern as the patterned layer.
 4. The patterned structureof claim 1, wherein the patterned structure is a free-standing structurethat is separated from the substrate.
 5. The patterned structure ofclaim 1, wherein the patterned structure is configured to be coupled toa base substrate.